In an electrophotographic process, charging devices are needed to uniformly charge various surfaces such as a photoreceptor, toner layer, intermediate belt, and/or media such as, paper. Conventional charging devices use high DC and AC voltages applied to a thin wire or pins to ionize air and produce charged particles (e.g., corotron, dicorotron). However, undesirable species such as ozone that have negative impact on the environment are also created as by-products. Previous efforts in making the charging process environmentally friendly included a bias charging roll process, a contact aquatron charging process, and more recently, a compact charging process with gas ions produced by electric field ionization from carbon nanotubes (CNT). The bias charging roll is a contact charging process. The direct contact of charging roll with photoreceptor causes both surfaces to wear. And even though, the bias charging roll process generates less ozone than a corotron or a dicorotron, it still generates a certain level of ozone. The aquatron charging process is also a contact process. Contact charging is not applicable to developed toner layer as required in an image-on-image development process. Although, CNT (or nanowire) emitter technology has been demonstrated in the literature, the precise fabrication of CNT (or nanowire) arrays at low cost is still in an early stage of research and not yet mature enough for producing reliable nano-charging devices at reasonable cost.
Accordingly, there is a need for a low cost, non-contact, compact, easy to manufacture, and environmentally friendly charging device.